24 cards where the set is “cmm” and (the collector number >= 668 and the collector number <= 691)

Kozilek, the Great Distortion (Commander Masters #668)
Morophon, the Boundless (Commander Masters #669)
Ulamog, the Ceaseless Hunger (Commander Masters #670)
Kemba, Kha Regent (Commander Masters #671)
Azami, Lady of Scrolls (Commander Masters #672)
Talrand, Sky Summoner (Commander Masters #673)
Urza, Lord High Artificer (Commander Masters #674)
Mikaeus, the Unhallowed (Commander Masters #675)
Shirei, Shizo's Caretaker (Commander Masters #676)
Grenzo, Havoc Raiser (Commander Masters #677)
Neheb, the Eternal (Commander Masters #678)
Azusa, Lost but Seeking (Commander Masters #679)
Omnath, Locus of Mana (Commander Masters #680)
Selvala, Heart of the Wilds (Commander Masters #681)
Gisela, Blade of Goldnight (Commander Masters #682)
Kykar, Wind's Fury (Commander Masters #683)
Maelstrom Wanderer (Commander Masters #684)
Meren of Clan Nel Toth (Commander Masters #685)
Slimefoot, the Stowaway (Commander Masters #686)
Tatyova, Benthic Druid (Commander Masters #687)
Teysa Karlov (Commander Masters #688)
The Ur-Dragon (Commander Masters #689)
Yuriko, the Tiger's Shadow (Commander Masters #690)
Zacama, Primal Calamity (Commander Masters #691)

The message was clear to Sorin—time to search for something else.